After Donald Trump attacked Marco Rubio on Twitter today, Rubio shot right back, giving the GOP front-runner a taste of his own medicine at a campaign rally in Dallas, Texas.

"It's time to pull [Trump's] mask off, so that people can see what we're dealing with here," Rubio told the crowd. "What we are dealing with here, my friends, is a con artist. He is a con artist."

He went on to mock Trump's Twitter attacks against him and said he had reached two conclusions as to why Trump included spelling errors in his vitriolic posts.

"Number one, that's how they spell those words at the Wharton School of Business where he went. Or number two, just like Trump Tower, he must have hired a foreign worker to do his own tweets," he said.

Rubio also went after Trump for the "Mr. Meltdown" insult, saying it was Trump who was having a meltdown last night.

"Let me tell you something, during one of the breaks, two of the breaks, he went backstage, he was having a meltdown. First, he had this little makeup thing applying, like makeup around his mustache, because he had one of those sweat mustaches. He wanted a full-length mirror. Maybe to make sure his pants weren't wet. I don't know," Rubio chided.

Rubio said Trump ran on the idea that he is fighting for the little guy, but that he's spent his entire career "sticking it to the little guy." Rubio argued that every business Trump has ever run has gone bankrupt, citing his casinos, Trump University and Trump Vodka.

The Florida senator encouraged people to go out and tell their friends not to vote for Trump. "Friends do not let friends vote for a con artist," he said.

Trump responded to Rubio Friday at a press conference ahead of his campaign rally in Texas, calling the Florida senator “desperate” and not “presidential material.”

“He is a pretty desperate guy. Down about 22 points in Florida,” Trump said.

Trump then offered his version of what happened backstage last night at the GOP debate.

“I'll tell you about backstage if you would like. I walked back there. He is with a pile of makeup, putting it on his face. Marco, easy with the makeup. You don't need that much. You know the story with Marco…He looked like he came out of a swimming pool. He was a mess,” Trump said.

Gov. Chris Christie of New Jersey endorsed Trump for president today, joining the New York businessman in Texas.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.